Multi-stage injector for thread withdrawal

ABSTRACT

A multi-stage injector for the suction withdrawal of a rapidly moving thread or filament exhibiting at least two suction conduits or tubes, each having an annular air injector at their discharge ends leading into the next suction conduit or a final mixing conduit which is preferably provided with a diffusor conduit at its discharge end.

United States Patent Ostertag et al.

[ MULTI-STAGE INJECTOR FOR THREAD WITHDRAWAL [72] Inventors: Karl Ostertag, Elsenfeld; Heinrich Nilgens,

Erlenbach/Main, both of Germany [73] Assignee: Akzona Incorporated, Asheville, NC.

[22] Filed: July 15, 1970 211 App]. 190.: 55,104

[30] 7 Foreign Application Priority Data July 19, 1969 Germany... P 19 36 916.5

-52 us. Cl ..226/097 51 Int. Cl. ..B65h 17/32 [58] Field of Search ..28/l.4, 22; 226/97, 7; 57/90 [451 'July 25,1972

[56] References Cited UNITED STATES PATENTS 3,559,860 2/1971 East ..226/97 3 ,423 ,000 1/1969 Heinen ..226/97 3,241,234 3/1966 Kiefer et a1. ..226/97 X Primary Examiner-Allen N. Knowles Assistant Examiner-Gene A. Church Attorney-Johnston, Root, O'Keeffe, Kell, Thompson & Shurtiefi" 57] i ABSTRACT A multi-stage injector for the suction withdrawal of a rapidly moving thread or filament exhibiting at least two suction conduits or tubes, each having an annular air injector at their .discharge ends leading into the next suction conduit or a final mixing conduit which is preferably provided with a diffusor conduit at its discharge end.

15 Claims, 4 Drawing Figures SHEE? 1 OF 2 INVEN'TORS. ARL OSTERTAG HEINRICH NILGENS ATT' YS PNENTEDJULZS m2 3,679.1 1

sum 2 er 2 KARL OSTERTAG HEINRICH NILGENS ATT'YS MULTI-STAGE INJECTOR FOR THREAD WITHDRAWAL In the production of artificial and especially synthetic thermoplastic polymer fibers or filaments, it is conventional when a disturbance occurs between the spinning nozzle and a winding or take-up device to pick up and draw off the rapidly running filamentary material by means of suction, usually by means of an injector in the shape of a rod or tube, for example, as the filamentary material collects in the blowing shaft situated beneath the spinning nozzles. Also, the resetting of a freshly spun thread or filament is normally carried out with such an injector. Moreover, it is possible where one wishes to stop a single spinning position, to draw off the running thread by means of an injector and thus immediately prevent the accumulation of thread within the spinning position.

Injectors for catching and drawing off a rapidly moving thread or similar filamentary material are generally known and normally employ air which is conducted at a high velocity past the discharge end of a suction conduit or tube, thereby creating a partial vacuum and drawing air at a high velocity through the inlet or feed end of the suction tube. This suction usually makes it quite easy to pick up the thread and transport it through the suction tube where it can be temporarily collected and held until the thread can be properly placed in the spinning operation, e.g. onto a take-up spool. However, it is essential that the injector be able to exert a sufficient tension or drawing force on the rapidly moving thread. It would also be desirable to have .an injector which operates with the highest possible efficiency, i.e. where the air consumption is as low as possible while the pressure loss inside the injector is also as low as possible, even when picking up and drawing off a thread moving at an extremely high velocity. Experience has shown, however, that existing injectors of this type are relatively inefficient and operate successfully only at a relatively low velocities of the rapidly moving thread.

For example, German Pat. No. 1,022,770 discloses a blowing or suction gun operating with compressed air, and according to the arrangement of a hand lever, this gun can be used as an injector for the drawing off of a thread or filamentary material under suction. Known draw-off guns or pistols of this type have only a single injection stage, and even when constructed with optimum design characteristics, they permit a drawing ofi of threads only at velocities of up to at most about 2,500 meters/minute. At such maximum thread velocities, such injector guns or pistols exhibit a very low efficiency as evidenced by high air consumption, high air pressures and correspondingly high pressure losses.

In a preliminary investigation leading to the present invention, it was found possible through certain modifications in the construction of such a single-stage injector to increase the drawing force or tension on the thread and also the efficiency of the injector such that threads could be drawn off with a velocity of up to 3,600 meters/minute. However, even these injectors were no longer suitable when it became necessary to draw off threads or filaments during the spin-stretching of textile yarn sizes at winding speeds of 4,000 meters/minute. Accordingly, it is quite apparent that a substantial improvement must be achieved with this type of thread injector if it is to be used under all conditions of thread velocity, i.e. even when the thread is moving at 4,000 meters/minute or at higher speeds.

One object of the present invention is to provide a thread injector in which the relative velocity between the thread and the air passing through the injector is as high as possible so as to be able to exert a sufficiently high tension or drawing force on the thread even in those cases where the thread velocity amounts to more than 4,000 meters/minute. Another object of the invention is to provide an injector which has the greatest possible efficiency, i.e. so as to achieve a maximum thread drawing capacity with the least consumption of air. Yet another object of the invention is to provide an injector which functions positively at all times and is easy to handle, especially for picking up and transferring a thread during a fully automatic spool change. These and other objects and advantages of the invention will become more apparent upon consideration of the following detailed specification.

It has now been found, in accordance with the invention, that a substantial improvement can be achieved in an injector for the suction withdrawal of a rapidly moving thread by providing a plurality of injection stages, i.e. a multi-stage injector having a plurality of interconnected, substantially coaxial, elongated air suction conduits, each of which is equipped with an annular air injection means around its thread discharge end, and a final elongated air mixing conduit in fluid communication with the annular air injection means of the last of the air suction conduits. The injector also preferably includes an air diffusor conduit which extends with a gradually increasing cross-section in the direction of air flow at the discharge end of the air mixing conduit.

It will be understood that such a multi-stage injector is one in which there is provided at least two mixing conduits as subsequent stages in addition to an initial suction conduit or first stage serving as the inlet for the rapidly moving thread as it is picked up by the injector, and it will be further understood that the mixing conduit of the first stage actually serves as a suction conduit for the second stage while the mixing conduit of the second stage serves as the suction conduit of the third stage, and so forth. For this reason, each stage or section of conduit having an annular air injection means around its thread discharge end may properly be considered as a suction conduit even though it may also serve as a mixing conduit for the preceding stage or section. Only the last mixing conduit, preferably with an attached diffusor conduit, serves as a final mixing stage where the thread is discharged from the multistage assembly without any further input of air and preferably with a reduction in the velocity of the air. Thus, regardless of whether one employs two or more stages, only the first stage requires a conduit which serves solely as a suction inlet for the thread and a last stage which serves only as a mixing conduit for the final discharge of the thread. All of the intermediate stages require a conduit functioning both as a suction conduit and a mixing conduit.

The term thread is employed herein in its broadest sense to include monofilaments as well as threads containing a plurality of individual filaments. However, the present invention is particularly adapted to handle melt-spun synthetic thermoplastic polymer filaments having a relatively small individual yarn size or denier, i.e. as conventionally produced in highspeed spinning operations for the production of textile filaments.

An especially preferred embodiment of the multi-stage injector according to the invention is illustrated by way of example in the accompanying drawing in which:

FIG. 1 is a schematic representation in longitudinal section of an injector having two stages, structural details having been omitted;

FIG. 2 is a partly diagrammatic and longitudinal sectional view of a preferred multi-stage injector as constructed in the form of a pistol or gun;

FIG. 3 is a side elevational view of the same two-stage injector pistol illustrating a thread receptacle for receiving thread from the outlet or discharge end of the injector; and

FIG. 4 provides a graphical representation to illustrate the manner in which the air consumption depends upon the tension or drawing force applied to the thread by the injector at a constant draw-off velocity.

Referring first to FIG. 1, one can readily follow the principles involved in the construction of a two-stage injector according to the invention. It should be noted that FIG. 1 is not drawn to scale and that certain portions and dimensions have been exaggerated in order to more clearly indicate the specific concepts involved. In general, the injector is constructed of a plurality of elongated and coaxial conduits or interconnected tubular members which preferably define a passageway of substantially circular cross-section which conically widens at the discharge end of the injector. The first stage of the injector essentially includes the suction tube 1 having an inside diameter d which is preferably between 3 mm. and 5 mm. in size, together with the first mixing tube 2 having an inside diameter 11 which is slightly larger than the outside diameter of the suction conduit 1 in order to provide an annular gap for the injection of air through the connected tube 5. The second stage of the injector is formed by the first mixing conduit 2 functioning as a second suction conduit together with the second or final mixing conduit 3, each of these conduits having the inner diameters 1 and d respectively. Again, the inner diameter d of the second mixing conduit 3 is larger than the outer diameter of the attached suction conduit 2 to permit the injection of air from tube 6 through an annular gap around the discharge end of the conduit 2. Each of the conduits 2 and 3, when functioning as a mixing device as between the injected air and the air flowing from the preceding suction conduit, should ordinarily be constructed in an elongated manner such that the effective length to diameter ratio has a minimum value of approximately 6, i.e. the effective length being designated by X and X, such that the ratio X :d X :d

The effective length of the first suction conduit 1 is designated by X while the length of the diffuser 4 is designated by X The diffusor has the same inner diameter as the final mixing conduit 3 where the two are joined together and then conically widens out to an inner diameter of d at the discharge end of the injector. The so-called diffusor angle" is designated by a and is preferably selected as an acute angle falling within the relatively narrow range of about 7.5 to 12.5".

In the operation of the multi-stage injector, a gaseous medium which is preferably compressed air is introduced at D and E with differing velocities and pressures such that the thread or filament 7 is drawn by suction in the direction of the arrows A, B and C. The compressed air D entering line 5 creates a suction in conduit 1 so that the thread is drawn into the device in the direction of the arrow A. The air introduced at A and B is then mixed in conduit 2 where a further suction is applied by the flow of compressed air E around the discharge end of conduit 2. A more detailed explanation of the injector in the form ofa suction gun and its operation follows hereinafter.

In its preferred construction as a suction gun or pistol as shown in FIG. 2 which can be held and operated with one hand, the multi-stage injector with its interconnected conduits 1, 2 and 3 together with the attached diffusor 4 and air feed lines 5, 6 are secured to a handle 8 having a relatively large bore or hollowed section 9 extending upwardly from the butt of the handle for the introduction of an initial supply of compressed air through any suitable outside feed line. An air distributor channel 11 is contained in the upper portion of the handle 8 and arranged adjacent to the initial feed channel 9 and in fluid connection therewith through the cylindrical bore or opening 20. The flow of compressed air F is controlled by the action of the valve which is shown axially seated in the bore and normally held in a closed position by the spring 12. The stem end of the valve 10 is actuated by the trigger or lever 13 which is pivoted on a blot 14 so that the valve can be easily opened while the suction gun is held in one hand. Instead of the conical valve 10 in bore 20, other suitable valve means can be provided to control the initial supply of compressed air.

The distributor channel 11 is connected to two individual air tubes, one of these tubes 5 supplying air to the first stage of the injector, and the other tube 6 connected over an orifice 15 to supply air to the second stage. It is advantageous to provide a variable orifice 15 wherein a size of the opening can be changed in a conventional manner from outside the handle. Alternatively, the handle 8 can be constructed so as to receive interchangeable orifices 15 of predetermined size. In this manner, the amount of air distributed between the individual air tubes 5 and 6 can be determined and adjusted quite accurately. When the trigger lever 13 is pressed to open the valve 10, the compressed air introduced at F immediately enters each stage of the injector and the thread or filament 7 is drawn in direction A through both stages so as to be discharged from the diffusor 4 in the direction C.

A slightly modified embodiment of the suction gun is illustrated in FIG. 3 wherein similar parts are identified by the same reference numerals as in FIG. 2, it being particularly advantageous to engage a suitable receptacle or collecting means 17 on the outlet end of the diffuser 4. This collector 17 can be connected to the diffuser 4 in a detachable manner by means of a hose clip 19 or other removable fastening means. In order to prevent the collector 17 from bending under the weight of the collected thread, it can be reinforced and supported by a basket or inner supporting means 18, for example in the form of a shaped wire mesh. This collector which is essentially a bag-like structure can be easily removed after it is filled with thread to the point where it might interfere with the operation of the injector, and there is nothing critical in the shape or size of the collector 17 provided that it is not so large as to interfere with the handling of the suction gun when being used by the operator. A suitable connecting nipple or coupling means 16 is provided at the base of the handle 8 in order to supply the propellant gaseous medium, preferably from a flexible hose or similar main feed line. It will be apparent that air is most economically employed as the gaseous medium under compression, although other gases could be employed if desired.

Depending upon the magnitude of the tension to be placed upon the moving thread or filament, which will vary with reference to the yarn size or denier of the thread and also with the velocity of the running thread, it will be obvious that the multi-stage injector of the invention can be constructed so as to provide more than two injection stages.

In order to substantiate the advantages of a multi-stage injector in accordance with the invention, the following discussion is oifered with particular reference to FIGS. 1 and 4 as well as the example set forth hereinbelow.

In order to produce the required tension or drawing force, which in the case of rapidly moving threads is correspondingly high, a certain relative velocity must be achieved between the thread and the gaseous medium passing through the injector so as to transport the thread by suction. This relative velocity is limited by the fact that with a constant throughput of the air mass in a tube, the Mach number in the direction of flow constantly increases as a result of pressure losses, but cannot exceed the value of 1. At the same time, however, the mean velocity in a short tube is higher than in a long tube. Accordingly, a multi-stage injector can be operated at a higher relative velocity than a single-stage injector with the same effective length of the injector. Furthermore, when using a multi-stage injector, only the last stage is traversed by the entire air mass, and the pressure losses are lower than in a sin glestage injector where the single mixing tube or conduit is traversed by the entire mass of air. This, in turn, means that with a multi-stage injector, even with the same capacity for transporting the thread, the air consumption will be lower and the efficiency of the injector greatly improved.

The efi'lciency of the multi-stage injector of the invention can be determined in accordance with the equation W.=(E VF/GJv A wherein:

2! [kg] is the sum ofthe thread forces ortension in kilograms (force) transmitted in each individual injector zone or stage.

Him/sec] is the thread velocityin meters per second; and

is the sum of the work done by the propellant air in the injector zones.

The most advantageous results are achieved with the multistage injector in terms of its efficiency by carefully dimensioning the suction conduit of the first stage. The determination of the optimum dimensions can be accomplished under certain simplifying conditions as explained in the example below.

Although it is sufficient if the multi-stageinjector merely consists of a first suction conduit and a number of sequential mixing conduits corresponding to the number of stages, i.e. so as to achieve a noticeable improvement in the efficiency of the injector, it is especially desirable for purposes of the invention in drawing off a very rapidly moving thread to provide the diffusor at the outlet or discharge end of the last mixing conduit. Also, where the thread velocity is approximately 4,000 meters/minute, a running speed which is of particular interest in the spinning and stretching of a synthetic thread, good results are achieved with an injector which is laid out in two stages, i.e. an injector which preferably consists of a suction conduit, a first mixing conduit (corresponding to a second suction conduit), a second or final mixing conduit and a diifusor.

The diffusor conduit of gradually enlarged cross-section in the direction of air flow has the function of raising the static pressure present at the end of the final mixing conduit to atmospheric pressure, this function being accomplished through retardation of the air flow velocity. From this function, one can determine the ratio of the cross-sectional area at the entry to the diffusor to its outlet area, and this ratio of course corresponds to the ratio of the inside diameters at the diffusor entrance and exit, i.e. the ratio d zd (see FIG. 1

The length of the diffusor X is determined from the preferred limits for the so-called diffusor angle i.e. the angle defined by the generatrix of the truncated cone of the diffusor, this angle also being referred to as the widening angle" or simply as the conical angle. As the diffusor angle is reduced below 75, the diffusor becomes relatively long and thereby causes high frictional losses which are undesirable in view of the higher pressures required. On the other hand, where the diffusor angle is above about l2.5, a retarded flow along the walls of the diffusor is no longer assured and the diffusion effect may be substantially reduced or even lost. It is for this reason that the diffusor angle preferably lies between about 75 and 125.

In addition, it is important that the flow velocity of the air at the diffusor exit should not fall below the thread velocity during the retardation of the air flow in the difi'usor, because otherwise the conveyance of the thread is inhibited. For this reason, the flow velocity of the air in the last mixing conduit must be maintained sufficiently high. This final flow velocity is therefore determined from the theorem of momentum for the mixing process. Since the propelled air flows only with the speed of sound into the mixing plane, the mixing speed can be influenced only by the amount of propelled air. In this manner, the inlet cross-section and the diameter of the final mixing conduit is established.

Although in theory the mixing process in each of the mixing conduits takes place in a single plane, actual practice has shown that it actually extends over a certain length of the mixing conduit. As a rule, the mixing is concluded after a length which corresponds to about six times the diameter of the mixing conduit. For this reason, the ratio of the length of each mixing tube to its inner diameter, i.e. each ratio X 11 X m or X d is preferably chosen so as to be equal to or greater than 6. On the other hand, this value should not be substantially greater than 6, since otherwise undesirable frictional losses again become too great.

As a general matter, the choice of the diameter of the first suction conduit should be considered on the basis that it ought to be as small as possible in order to reduce the amount of air being drawn into and carried along through the injector. At the same time, however, in order to exclude disturbances in the flow behavior or transport of the running thread, excessively narrow suction tubes or conduits should be avoided. It has therefore been found most expedient to select an inner diameter d of the first suction conduit of between about 3 mm. and 5 mm.

The general size and shape of the entire injector in the form of a suction gun or pistol, including the air feed lines, can be easily determined in a routine manner. The bag or container attached onto the diffusor should be reasonably well supported in order to prevent a bending down of the bag which may cause a substantial reduction in the suction effect. Any

sturdy wire or plastic supporting structure in the form of an open-mesh basket can be used for this purpose. Of course, this bag must be reasonably porous or contain openings at suitable locations so as to permit the discharge of air to the surrounding atmosphere.

The following working example is offered for purposes of comparison of the efficiency of the multi-stage injector of the invention with a single-stage injector.

EXAMPLE The optimum construction and dimensions of both a twostage injector and a single-stage injector can be easily determined in a conventional manner, for example in accordance with the mathematical and physical relationships as set forth in the manuscript of W. J. Beck and D. B. Holmes, Fysisch- Technologische Aspecten Van de Polymerwerking, TH Delft 1964/1965 in conjunction with G. N. Abromowitsch, Angewandte Gasdynamik, VEB Verlag Technik, Berlin. For the two-stage injector employed in this example, the mixing conduit of the first stage is regarded as the suction conduit of the second stage, and both stages are treated in a corresponding manner, and the assumption is also made that the thread consists of densely packed individual filaments.

The example is carried out in a test using a rapidly running thread in a stretch-spinning machine having a draw-off velocity of 4,000 meters/minute, the thread having a total yarn size of 45 denier l 3 individual filaments) which corresponds to dtex 50 f 13.

The following table sets forth all of the necessary data acquired in the test, both as to the dimensions of the multistage injector and also those measurements required to determine the efficiency of the two-stage injector.

TABLE I Suction pressure V l60'm/sec.

V 66.67 m/sec. d =4 mm. X 70 mm.

AP, 604 k /m P,,= A 9,726 k m inner diameter d 10 mm. Velocity in lst mixing tube V 243.3 m/sec. Length of lst mixing tube X 60 mm.

Pressure loss Ap 272 kg/m Static pressure at end of lst mixing tube Static pressure Initial feed air pressure 2nd mixing tube P3 P2 Pa 7,384 81 p =p 7,884 kg/m P 14,932 kg/m inner diameter d; 17 mm. Velocity in 2nd mixing tube V,, 270 m/sec. Length of 2nd mixing tube X mm.

Pressure loss Ap 277 kg/m Static pressure at end of 2nd mixing tube Total pressure Diffusor pressure loss P P AP 7,607 kg/m p 10,899 kg/m Ap 122 kg/m Exit diameter d 24.9 mm. Length of diffusor X 45.4 mm. Hydraulic radius of the thread r 202 um.

Transmitted tension Transmitted tension Transmitted tension Total tension (The increase in tension in the zone of the diffusor has been neglected.)

Total efficiency of the two-stage injector:

In regard to the data appearing in the above table, it is to be noted that the indices relate to the following cross-sections (FIG. 1):

Index 2:

Index 3:

Index 4:

Index 5:

Index 6:

Index D and Index E relate to the cross-sections of the air feed lines 5 and 6, respectively.

A comparison between a single-stage and a two-stage injector is further presented in the following table:

TABLE II Injector 2-stage 1 -stage Efficiency 0.166 0.09 Tension (kg) 3.2-10 2.3'10 Admissible thread velocity (m/min.) 4,000 3,600 Air consumption (Nm /h) 133.5 I41 Likewise FIG. 4 can be observed for comparison of the twostage injector with the single-stage injector. In this graph, the air consumption [Nm /h] is plotted against the tension [P]. The broken line for the two-stage injector lies considerably lower and runs-less steeply than the solid line for the singlestage injector. This means that the two-stage injector with equal tension has a considerably lower air consumption and that with increase of the necessary tension the air consumption increases less strongly than in the case of the single-stage injector. Accordingly, the two-stage injector provides a considerably better efficiency.

The Invention is hereby claimed as follows:

1. A multi-stage injector for the suction withdrawal of a rapidly moving thread which comprises:

a plurality of interconnected, substantially coaxial, elongated air suction conduits, each having an annular air injection means around its thread discharge end for introducing compressed air and causing a suction throughout the suction conduits sufficient to transport a thread therethrough; and

a final elongated air mixing conduit in fluid communication with the annular air injection means of the last of said air suction conduits.

2. An injector as claimed in claim 1 wherein an air difiusor conduit extends with a gradually increasing cross-section in the direction of air flow at the discharge end of said air mixing conduit.

3. An injector as claimed in claim 1 having two interconnected air suction conduits followed by said final air mixing conduit.

4. An injector as claimed in claim 3 wherein an air diffusor conduit extends with a gradually increasing cross section in the direction of air flow at the discharge end of said air mixing conduits, and all of said conduits define a passageway of substantially circular cross-section which conically widens in the diffusor conduit.

5. An injector as claimed in claim 4 wherein the conical angle of the diffuser conduit is between about 7.5 and An injector as claimed in 01mm 4 wherein the ratio of lengthzdiameter for each suction conduit and mixing conduit following the first suction conduit is approximately 6:1.

7. An injector as claimed in claim 4 wherein the diameter of the passageway in the first suction conduit receiving the moving thread is about 3 to 5 mm.

8. An injector as claimed in claim 4 constructed in the form of a pistol having handle means connected to said conduits arranged as the barrel of the pistol.

9. An injector as claimed in claim 8 wherein said handle means encloses a valve operated air distributor channel with means on one side of said valve for fluid connection to an air supply line and individual air tubes on the other side of said valve for the distribution of the supplied air to each of said annular air injection means.

10. An injector as claimed in claim 9 wherein said valve is mounted in said handle for movement from a closed to an open position by a trigger lever connected thereto.

II. An injector as claimed in claim 4 wherein an enlarged receptacle is mounted onto the widened discharge end of said air diffusor conduit for the reception and temporary storage of a withdrawn length of thread.

12. An injector as claimed in claim 4 wherein the first suction conduit has an inner diameter of about 3 to 5 mm., each succeeding suction conduit and mixing conduit has a ratio of lengthzdiameter of approximately 6, and the conical angle of the difiusor conduit is between about 7.5 and 12.5.

13. An injector as claimed in claim 12 which includes an air supply means controlled by a trigger operated valve to supply air under high pressure to each of said annular air injection means.

14. An injector as claimed in claim 1 wherein the ratio of lengthzdiameter for each suction conduit and mixing conduit following the first suction conduit is at least about 6:1.

15. An injector as claimed in claim 1 including a valve operated air distributor channel with means on one side of said valve for fluid connection to air supply line and individual air tubes on the other side of said valve for the distribution of the supplied air to each of said annular air injection means.

"M050 UNITED STATES PATENT FICE 5 69) CERTIFICATE OF' CORRECTION Pacem; No. 11L" D d y 5, 97

Ostertag et a1 Inventofls) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

rColumn 3, line 16, reads x zd I x :d I 6. ",should' "'3 read x zd I x zd Column 4, line. 56, reads "V 1 (EP'V /Ge/' 'Ap' 100(%) should inj f read tum P'Vf A lOO(%) Signed and 'seal ed this 20th day of March 1973.

(SEAL) Attest EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. A multi-stage injector for the suction withdrawal of a rapidly moving thread which comprises: a plurality of interconnected, substantially coaxial, elongated air suction conduits, each having an annular air injection means around its thread discharge end for introducing compressed air and causing a suction throughout the suction conduits sufficient to transport a thread therethrough; and a final elongated air mixing conduit in fluid communication with the annular air injection means of the last of said air suction conduits.
 2. An injector as claimed in claim 1 wherein an air diffusor conduit extends with a gradually increasing cross-section in the direction of air flow at the discharge end of said air mixing conduit.
 3. An injector as claimed in claim 1 having two interconnected air suction conduits followed by said final air mixing conduit.
 4. An injector as claimed in claim 3 wherein an air diffusor conduit extends with a gradually increasing cross-section in the direction of air flow at the discharge end of said air mixing conduits, and all of said conduits define a passageway of substantially circular cross-section which conically widens in the diffusor conduit.
 5. An injector as claimed in claim 4 wherein the conical angle of the diffusor conduit is between about 7.5* and 12.5* .
 6. An injector as claimed in claim 4 wherein the ratio of length:diameter for each suction conduit and mixing conduit following the first suction conduit is approximately 6:1.
 7. An injector as claimed in claim 4 wherein the diameter of the passageway in the first suction conduit receiving the moving thread is about 3 to 5 mm.
 8. An injector as claimed in claim 4 constructed in the form of a pistol having handle means connected to said conduits arranged as the barrel of the pistol.
 9. An injector as claimed in claim 8 wherein said handle means encloses a valve operated air distributor channel with means on one side of said valve for fluid connection to an air supply line and individual air tubes on the other side of said valve for the distribution of the supplied air to each of said annular air injection means.
 10. An injecTor as claimed in claim 9 wherein said valve is mounted in said handle for movement from a closed to an open position by a trigger lever connected thereto.
 11. An injector as claimed in claim 4 wherein an enlarged receptacle is mounted onto the widened discharge end of said air diffusor conduit for the reception and temporary storage of a withdrawn length of thread.
 12. An injector as claimed in claim 4 wherein the first suction conduit has an inner diameter of about 3 to 5 mm., each succeeding suction conduit and mixing conduit has a ratio of length:diameter of approximately 6, and the conical angle of the diffusor conduit is between about 7.5* and 12.5* .
 13. An injector as claimed in claim 12 which includes an air supply means controlled by a trigger operated valve to supply air under high pressure to each of said annular air injection means.
 14. An injector as claimed in claim 1 wherein the ratio of length:diameter for each suction conduit and mixing conduit following the first suction conduit is at least about 6:1.
 15. An injector as claimed in claim 1 including a valve operated air distributor channel with means on one side of said valve for fluid connection to air supply line and individual air tubes on the other side of said valve for the distribution of the supplied air to each of said annular air injection means. 